OK
Go to the drug store and get a small bottle of silver nitrate. Put a few drops on a place that you cannot see. If magnesium it will turn black. Aluminum does nothing.
Or go buy some distilled white vinegar. Put some on a hided place. if Magnesium the piece will bubble aluminum will not.
My last option is for you to go to a pool supply and buy a magnesium test kit and put a few file shavings in water and test.
Whip
Where is shop tip section?